The present invention relates to an automatic diaphragm aperture control device for use in a camera.
More particularly, the present invention relates to improvements in an automatic diaphragm aperture control device which controls the diaphragm aperture with a high accuracy so as to provide an optimum exposure with respect to the brightness of an objective image and a pre-selected shutter speed.
An exposure control device is already known which automatically controls a diaphragm aperture so as to provide an optimum exposure with respect to the measured brightness of an objective image and the pre-selected shutter speed. This operation will be referred to hereinafter as "auto-stopping down opertion". There is also known an exposure control device which automatically controls the shutter speed so as to provide an optimum exposure with respect to a setting of the diaphragm aperture which has been selected beforehand, where the control of the shutter speed is made in dependence upon a measurement of the brightness of an objective image.
U.S. Pat. No. 3,777,637 discloses an example of such an auto-stopping down device. In the device disclosed by this patent, the light from an objective image which has passed through the objective lens and the aperture of the diaphragm is measured, with the diaphragm being stopped down from its open position, before the exposure operation is started, in association with the releasing operation of the shutter. When an output signal indicative of the light measurement reaches an optimum value relative to the preselected shutter speed, the diaphragm is locked so as to stop its stopping down operation. This operation thereby controls the setting of the diaphragm aperture.
In utilizing the above-described auto-stopping down operation, the advantage is achieved that a known exchangeable lens which is available in the market may be used intact in conjunction with the auto-stopping down operation. In this operation, upon control of the diaphragm aperture by locking the diaphragm so as to stop its stopping down operation, an actuating signal is generated at the time when the diaphragm aperture provides an optimum exposure relative to the pre-selected shutter speed. Upon receipt of this actuating signal the diaphragm is locked by means of a locking mechanism, which was previously in a retracted position from the stopping down mechanism. This operation, however, results in the disadvantage of the occurrence of a time delay due to the movement of the locking mechanism and the operations of the other mechanical members. This time delay causes the diaphragm to be actually stopped down to an additional extent as compared with the diaphragm aperture setting which would provide an optimum exposure.